As illustrated in FIGS. 8 and 9, a known fuel cell (a unit fuel cell) 1 includes a membrane-electrode assembly (MEA) and a separator 2 disposed on each side of the MEA. A plurality of fuel cells 1 are piled to construct a layer-type fuel cell or a stack. A gas passage 3 is formed in the separator 2 at an MEA opposing surface of the separator 2 and a coolant passage 4 is formed in the separator 2 at an opposite surface of the MEA opposing surface of the separator. A gas seal 5 is disposed for seal between the separators on opposite sides of the MEA and between the separator and the MEA, a coolant seal 6 is disposed for seal between adjacent fuel cells.
As illustrated in FIG. 8, in a case where a seal line of the gas seal 5 around a fuel gas manifold 7, an oxidant gas manifold 8, and a coolant manifold 9 which receives a gas pressure on an MEA opposing side thereof does not extend straight (more particularly, in FIG. 8, since the coolant manifold 9 has a greater width than the gas manifolds 7 and 8, a portion of the seal line of the gas seal 5 beside the coolant manifold 9 is bent and is bulged toward a central portion of a fuel cell surface and so does not extend straight), and in a case where the separator 2 is deformable (such as a carbon separator or a metal separator of about 0.1 mm thickness), the separator 2 experiences a deformation when a gas pressure acts on the separator and the gas seal 5 receives a stress due to the deformation of the separator 2 locally (for example, at a corner “B” of the seal line in FIG. 8). As a result, the gas seal 5 is separated from the separator 2 to generate a possibility of gas leakage.
Further, as illustrated in FIG. 8, a portion of the seal line of the coolant seal 6 does not exist at a connecting coolant passage “C” between the coolant manifold 9 and the coolant passage of the central portion of the fuel cell. As a result, at a portion “D” of FIG. 9 opposite to the passage “C” via the separator 2, a seal force (a fastening force of the stack of fuel cells) does not act on the gas seal 5 and the gas pressure is resisted only by an adhering force of the gas seal 5. Therefore, the gas seal 5 is likely to be separated from the separator 2 when the separator 2 is deformed due to receiving a gas pressure, thereby generating a possibility of gas leakage.
Japanese Patent Publication 2002-124275 discloses a seal structure where a gas manifold and a coolant manifold have the same width. In such a structure, a design that a seal line extends straight and a gas seal line and a coolant seal line are overlapped in a fuel cell stacking direction can be easily adopted.
However, even by the seal structure of Japanese Patent Publication 2002-124275, the problem of the passage “C” of FIG. 8 cannot be solved. More particularly, since no gas seal and no coolant seal exist for allowing gas and coolant to flow at the connecting gas passage between the gas manifold and the gas passage of the central portion of the fuel cell and at the connecting coolant passage between the coolant manifold and the coolant passage of the central portion of the fuel cell, the gas seal and the coolant seal cannot operate as a back-up to each other at the connecting gas passage and the connecting coolant passage. As a result, the problem that when a gas pressure acts on the separator, the separator is deformed and the seal is separated from the separator to generate leakage still remains.
Further, in the fuel cell disclosed in Japanese Patent Publication 2002-124275, the gas manifold and the coolant manifold have the same width and the gas seal line and the coolant seal line happen to be overlapped in the fuel cell stacking direction. However, in the fuel cell illustrated in FIG. 8 where the width of the gas manifold and the width of the coolant manifold are different from each other, usually the gas seal line and the coolant seal line cannot be overlapped in the fuel cell stacking direction. As a result, the problem of the portion “B”, that is, the problem that the seal line is bent and when the separator is deformed locally, the seal is separated from the separator to cause leakage, cannot be solved.
Document US 2003/0091885 A1 discloses an electrolyte membrane-gasket assembly for a fuel cell, including a polymer electrolyte membrane and a gasket, made of a seal material, covering the peripheral portion of the electrolyte membrane, in which the electrolyte membrane has a sequence of a plurality of through-holes in the peripheral portion, and a portion of the gasket covering one surface of the electrolyte membrane and a portion covering the other surface are connected to each other through the through-holes of the electrolyte membrane.
Document US 2003/0186106 A1 discloses a fuel cell stack comprising a plurality of fuel cells, each having an anode flow field plate, a cathode flow field plate and a membrane electrode assembly disposed between the flow field plates. The anode and cathode flow field plates have primary channels and ribs separating the primary channels. At least a portion of the anode and cathode primary channels are disposed directly opposite one another with a membrane exchange assembly therebetween and with at least some of the ribs on the anode and cathode flow field plates located directly opposite one another to sandwich the membrane exchange assembly therebetween.
Document US 2002/0182471 A1 discloses a sealing method and apparatus for a fuel cell stack that includes a stack of flow plates, a first gasket that is compatible with a coolant and a second gasket that is incompatible with coolant. The first gasket forms a seal around a coolant manifold passageway between an adjacent pair of plates. At least one region of a particular plate may be associated with a reactant flow, and this plate may include internal passageways that extend between manifold passageways to communicate a coolant. A seal that is substantially permanent isolates the internal passageways from the regions of the fuel cell plate that may be associated with reactant flows.
Document US 2003/0072988 A1 discloses seals for fuel cells and fuel cell stacks, wherein in a fuel cell stack assembly having a plurality of plates with grooves for accommodating gaskets. Seals are provided between individual fuel cell plates in the fuel cell stack assembly in order to prevent leakage of gases and liquids required for operation of the fuel cell stack assembly.
Document US 2002/0031698 A1 discloses a fuel cell having sealant for sealing a solid polymer electrolyte membrane, wherein a seal contacts the projecting portion which extends from the solid polymer electrolyte membrane and which projects from the peripheries of the anode side diffusion electrode and the cathode side diffusion electrode while the membrane electrode assembly is disposed between the separators.
Document EP 1 302 996 A2 discloses a polymer electrolyte fuel cell comprising a unit cell comprising a membrane electrode assembly (MEA) comprising a polymer electrolyte membrane, a gasket covering the periphery of the electrolyte membrane, an anode and a cathode attached to the electrolyte membrane; and conductive separator plates sandwiching the MEA therebetween.
Document US 2002/0122970 A1 discloses a method for fabricating a seal-integrated separator for a fuel cell, wherein a seal-integrated separator having first to fourth seals which are integrated on both sides of the separator body is fabricated.
A first problem to be solved by the present invention is that at the gas and coolant connecting passages between the gas and coolant manifolds and the gas and coolant passages at the central portion of the fuel cell, one of the gas seal and the coolant seal at the opposite sides of the separator is not provided. As a result, the gas seal and the coolant seal at the opposite sides of the separator cannot operate as a back-up to each other, and sealing characteristic and stability of the seal on a backside of the interrupted seal portion are degraded.
A second problem to be solved by the present invention is that, in addition to the first problem, in the case where the width of the gas manifold and the width of the coolant manifold are different from each other, the gas seal line and the coolant seal line are not overlapped to each other, and sealing characteristic and stability of the non-overlapped portion of the seal line are degraded.